KR101724755B1 - Methods for preparing composition, sheet comprising the composition and electrode comprising the sheet - Google Patents

Abstract

Providing a mixture of carbon particles and a solvent and shearing the mixture to form a dispersion of the carbon particles in the solvent; Adding non-fibrillated poly (tetrafluoroethylene) to said dispersion to provide a product mixture and shearing said product mixture until at least a portion of said poly (tetrafluoroethylene) is fibrillated; Processing the product mixture into a sheet; And bonding the sheet onto a current collector. Methods for producing the electrode sheet and the sheet composition are also provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a composition, a sheet containing the composition, and a method of manufacturing an electrode including the sheet.

Field of the Invention This invention relates generally to electrodes, and more particularly to a composition comprising a sheet comprising the composition, and an electrochemical device comprising the sheet and including a supercapacitor, a fuel cell, and a supercapacitor desalination device And a method of manufacturing an electrode to be used.

Supercapacitors are energy storage devices with high capacitance per unit mass and high instantaneous non-output (of the order of tens to about 100 farads (F / g) of active material per gram). The supercapacitor electroadhesion deionization method has recently been proposed as a new desalination technology that reduces water treatment costs and prevents environmental pollution.

The supercapacitor includes two identical electrodes, an electrolyte, and a separator interposed between the electrodes and permeable to the electrolyte ions. Supercapacitors are classified into different types depending on the structure of the electrodes and the characteristics of the electrolytes. One type of supercapacitor has an organic electrolyte and an activated carbon electrode with a large specific surface area of 1000 to 3000 m2 / g and is electrostatically driven.

The activated carbon electrode of the supercapacitor is obtained by depositing a paste sheet on a current collector. The paste is a mixture of activated carbon, a solvent and a binder. Polytetrafluoroethylene (PTFE) is a commonly used electrode binder.

In preparing the paste sheet, PTFE, carbon and solvent are mixed at high shear and high temperature, uniaxially calendered at high temperature, extruded to a final form at high temperature, and dried at high temperature to remove the solvent. High temperatures, especially temperatures close to the boiling point of water, can cause water loss to occur rapidly. As the water is lost, the viscosity of the material rises in an uncontrolled manner, the fibrillation rate of PTFE rises sharply, and it is difficult to fibrillate the PTFE to a consistent level. Drying also causes water to be removed as steam, which is entrained in very small pores in and around the carbon particles. In general, it takes a very long time to rewet the carbon PTFE material, and even some of the original wetted internal pores of the carbon PTFE material can not be rewet again.

It has been proposed to carry out this operation at room temperature at low shear rates and without drying. However, this method produces poor electrode sheets because all the materials are mixed in one step (one-step method), resulting in non-uniform mixing of PTFE and poor fibrillation of PTFE. Moreover, this method usually takes a relatively long time.

Thus, there is a need for improved processes for the composition, the sheet comprising the composition, and the electrode comprising the sheet.

In one embodiment, providing a mixture of carbon particles and a solvent and shearing the mixture to form a dispersion of the carbon particles in the solvent; And adding the non-fibrillated poly (tetrafluoroethylene) to the dispersion to provide a resulting mixture and shearing the resulting mixture until at least a portion of the poly (tetrafluoroethylene) is fibrillated ≪ / RTI > is provided.

In another embodiment, there is provided a process for preparing a dispersion of carbon particles, comprising: providing a mixture of carbon particles and a solvent and shearing the mixture to form a dispersion of the carbon particles in the solvent; Adding non-fibrillated poly (tetrafluoroethylene) to said dispersion to provide a product mixture and shearing said product mixture until at least a portion of said poly (tetrafluoroethylene) is fibrillated; And a step of processing the product mixture into a sheet.

In another embodiment, there is provided a process for preparing a dispersion of carbon particles, comprising: providing a mixture of carbon particles and a solvent and shearing the mixture to form a dispersion of the carbon particles in the solvent; Adding non-fibrillated poly (tetrafluoroethylene) to said dispersion to provide a product mixture and shearing said product mixture until at least a portion of said poly (tetrafluoroethylene) is fibrillated; Processing the product mixture into a sheet; And bonding the sheet onto a current collector.

The following is an exemplary embodiment and reference is made to the similar numbered figures for similar elements.
1 is a scanning electron micrograph of the composition prepared in Example 1. Fig.
2 is a scanning electron micrograph of the sheet produced in Example 1. Fig.
3 is a scanning electron micrograph of the composition prepared in Comparative Example 1. Fig.
4 is a scanning electron micrograph of the sheet produced in Comparative Example 1. Fig.

A composition, a sheet comprising the composition, and methods of making the electrode comprising the sheet are described herein. The electrode may be used in an electrochemical device such as a supercapacitor, a fuel cell, and a supercapacitor desalination.

Providing a mixture of carbon particles and a solvent and shearing the mixture to form a dispersion of the carbon particles in the solvent; And adding the non-fibrillated poly (tetrafluoroethylene) to the dispersion to provide a resulting mixture and shearing the resulting mixture until at least a portion of the poly (tetrafluoroethylene) is fibrillated (2-step method). After calendering, printing and / or extrusion, the resulting mixture is processed into a sheet. The sheet is trimmed to a desired size and shape and is pressed onto the current collector to form an electrode.

The resulting mixture is dried in an oven at 100 < 0 > C and is compacted (5 MPa) into small pieces. The sheet is cut into small pieces. These small pieces can be used for scanning electron microscopic characterization.

The solvent may be water, ethanol, or any other suitable solvent. As the conductive material may be included in the mixture, the composition may comprise from 2 to 10% (by dry weight) of poly (tetrafluoroethylene); 0 to 30% (by dry weight) of conductive material; And 60 to 98% (by dry weight) of carbon particles. The conductive material may be a strongly acidic cation exchange resin, a strong basic anion exchange resin, a carbon black, a graphite powder, or the like. The non-fibrillated poly (tetrafluoroethylene) is added portionwise in the fraction. It should be noted that ion exchange resins dramatically improve the performance of the electrode by, for example, increasing the capacity by 37% and / or reducing the resistance by, for example, 21%. The weight ratio between water and the total amount of fibrillatable PTFE, conductive material and carbon particles may be from 3: 2 to 4: 1. The amount of solvent affects the manner in which the composition is processed into a sheet. If the amount of solvent used is small, the composition should be calendared to a sheet. If the amount of solvent used is high, the product mixture can be printed directly onto the current collector.

The front end is a speed mixer (e.g., Speedmixer (TM) DAC (Dual Asymmetric Centrifuge) 150 FVZ, Siemens) based on biaxial rotation of a mixing arm and a basket inside the mixing arm, Type. The mixing arm of the DAC 150 FVZ rotates at a speed of up to 3500 rpm in one direction. The bathket rotates in the opposite direction at a speed of about 900 rpm. The combination of different centrifugal forces acting in different directions enables a fast mixing process. The shear speed used in this application is 400 to 3500 rpm (rotation of the mixing arm).

The viscosity analysis is a powerful tool in investigating the physical properties of PTFE in the mixture. According to the viscosity analysis, the PTFE increases the viscosity during the mixing process due to the fibrillation of the PTFE, which viscosity is dependent on the shear rate and shear time, thus indicating that the degree of fibrillation is likewise increased. Because shear breaks the fiber as the time elapses, the viscosity decreases with time, even if the shear rate is too high. Thus, a relatively short shear time is sufficient to fibrillate at high shear rates. Therefore, the production process is carried out at room temperature within 0.5 to 10 minutes.

The tensile strength of the sheet is tested by a SANS CMT5105 electromechanical general purpose testing machine using a dumbbell-shaped sample having a width of 4 mm and a thickness of 1 mm.

The singular forms as used herein are not intended to limit the quantity, but merely indicate that at least one reference item is present. Also, endpoints of all ranges for the same component or characteristic include their endpoints, but can be combined independently (e.g., "up to about 25 weight percent, or more specifically about 5 to about 20 weight percent" Endpoints and all intermediate values in the range "about 5 to about 25% by weight"). Throughout this specification, terms such as " one embodiment ", "another embodiment "," certain embodiments ", and the like refer to elements (e.g., features, structures, and / or properties) described in connection with the embodiments Quot; is included in one or more embodiments described herein, and may or may not be present in other embodiments. It should also be appreciated that the elements described above may be combined in any suitable manner in various embodiments. Unless defined otherwise, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Example

Next, the present invention will be described concretely with reference to Examples and Comparative Examples.

Example 1

Activated carbon (12 g, manufactured by Yuhuan activated carbon Co. Ltd., average particle size 15 microns, surface area 2000 m2 / g) and 38 g of water were added to the speed mixer. 1000 rpm for 30 seconds at room temperature.

Then 0.6 g of PTFE (T-60 emulsion, Dupont) was added dropwise to the mixture and mixed for 30 seconds at 1000 rpm. Another 0.6 g of PTFE was added to the mixture and mixed at 1000 rpm for 30 seconds. The resulting mixture was then formed as a paste, and some of the water exuded from the mixture. This paste can be used directly for calendering without any drying step.

1 is a scanning electron microscope (SEM) photograph of the paste. From this photo, fibers were found near the carbon particles. This confirmed that fibrillation of PTFE occurred during mixing.

For roll calendering, a 2-roll calender was used. The calender nip was set to 0.8 mm width, and the mixed paste was passed through the nip to form a thin sheet. This sheet was folded in 1/3 and then inserted again into the nip of the calendar. This process was repeated five times while changing the rolling direction at 90 ° each time. Finally, a uniform thin carbon composite sheet having a thickness of about 1 mm was prepared. Fig. 2 shows an SEM photograph of the carbon sheet produced by this method. It is very clear that the carbon particles are surrounded by PTFE fibers. These fibers were elongated in several directions compared to the disorder of the paste before calendering. This oriented fiber stretch is due to the calendering process. The tensile strength of the resulting sheet is 0.14 MPa.

Finally, the sheet was trimmed to a 4 cm x 10 cm rectangle for use in an electrode assembly. One rectangle was placed on the Ti mesh collector. After compression (8 MPa), a capacitor electrode having a surface area of 40 cm < 2 > was formed. Two electrodes with two stacked spacers (1.0 mm thick) each having an active carbon loading of 3 g were assembled together to form a cell for use in supercapacitor desalination. There is a 1560 ppm NaCl solution between these electrodes. The cell resistance was 2.4 +/- 0.07 Ohm. The cell capacity was 75.6 ± 0.7 F / g and was measured by scanning cyclic voltammetry in 1 mol / L NaCl solution.

Example 2

(6 g, manufactured by Yufuin Activated Carbon Co., Ltd., coconut shell type, average particle size 15 microns, surface area 2000 m2 / g) and 21 g of anion exchange resin (Tianjin Nankai Resin Factory, strong basic anion exchange resin 201X7, milled to about 5 ㎛ before use, moisture content 40%) and 20 g of water were added to the speed mixer. 1000 rpm for 30 seconds at room temperature.

To the mixture, a total of 0.8 g of PTFE (T-60 emulsion, DuPont) was added. 0.2 g of PTFE was added dropwise to the mixture each time and mixed for 20 seconds at 3500 rpm until completion. This paste was placed directly on the roller for calendering.

For roll calendering, a 2-roll calender was used. The calender nip was set to a width of 0.8 mm and the mixed paste was passed through the nip to form a thin sheet which was folded in 1/3 and again inserted into the nip of the calender. This process was repeated five times while changing the rolling direction at 90 ° each time. Finally, a uniform thin carbon composite sheet having a thickness of about 1 mm was prepared.

Finally, the sheet was trimmed with a 4 cm x 10 cm rectangle for use in an electrode assembly, which was then placed on a Ti mesh housing. After compression (8 MPa), a capacitor electrode was formed. An electrode having an active carbon loading of 3 g was assembled as a positive electrode for use in supercapacitor desalination.

Example 3

(6 g, produced by Yufuin Activated Carbon Co., Ltd., coconut shell type, average particle size 15 microns, surface area 2000 m2 / g) and 21 g of cation exchange resin Exchange resin 001X7, milled to about 5 [mu] m before use, moisture content 40%) and 20 g of water were added to the speed mixer. 1000 rpm for 30 seconds at room temperature.

To the mixture, a total of 0.8 g of PTFE (T-60 emulsion, DuPont) was added. Each time 0.2 g of PTFE was added to the mixture and mixed for 20 seconds at 3500 rpm until completion. This paste was placed directly on the roller for calendering.

For roll calendering, a 2-roll calender was used. The calender nip was set to a width of 0.8 mm and the mixed paste was passed through the nip to form a thin sheet which was folded in 1/3 and again inserted into the nip of the calender. This process was repeated five times while changing the rolling direction at 90 ° each time. Finally, a uniform thin carbon composite sheet having a thickness of about 1 mm was prepared.

Finally, the sheet was trimmed with a 4 cm x 10 cm rectangle for use in an electrode assembly, which was then placed on a Ti mesh housing. After compression (8 MPa), a capacitor electrode was formed. An electrode having an active carbon loading of 3 g was assembled as a cathode for use in supercapacitor desalination.

The cathode (40 cm2 surface area) of Example 3 produced above and the anode (40 cm2 surface area) of Example 2 were assembled together and two spacers (thickness: 1.5 mm) were placed between these electrodes. The cell resistance was measured by calculating the voltage at the start of the charge state in 1560 ppm NaCl solution. Then, the capacity was measured in a 1 mol / L NaCl solution by scanning cyclic voltammetry. The cell resistance was 1.9 ± 0.10 Ω. Was reduced by 21% as compared with Example 1. The specific capacity was 103 ± 0.5 F / g, which was increased by 37% as compared with Example 1.

Example 4

Activated carbon (12 g, manufactured by Yufuang Activated Carbon Co., Ltd., coconut shell type, average particle size 15 microns, surface area 2000 m2 / g) and 35 g of ethanol were added to the speed mixer. 1000 rpm for 30 seconds at room temperature.

To the mixture, 1.6 g of PTFE (T-60 emulsion, DuPont) was added dropwise three times. Specifically, a first 0.4 g PTFE was added to the mixture and mixed at 800 rpm for 1 minute; Then 0.6 g of PTFE was added dropwise to the mixture and mixed at 800 rpm for 1 minute; Finally 0.6 g of PTFE was added to the mixture and mixed for 1 minute at 800 rpm. The resulting paste was used for calendering.

For roll calendering, a 2-roll calender was used. The calender nip was set to a width of 0.8 mm and the mixed paste was passed through the nip to form a thin sheet which was folded in 1/3 and again inserted into the nip of the calender. This process was repeated five times while changing the rolling direction at 90 ° each time. Finally, a uniform thin carbon composite sheet having a thickness of about 1 mm was prepared.

Finally, the sheet was trimmed with a 4 cm x 10 cm rectangle for use in an electrode assembly, which was then placed on a Ti mesh housing. After compression (8 MPa), a capacitor electrode was formed. The formed cell was used for supercapacitor desalination.

Comparative Example 1

12 g of activated carbon (manufactured by Yufu Activated Carbon Co., Ltd., coconut shell type, average particle size 15 microns, surface area 2000 m2 / g), 38 g of water and 1.2 g of PTFE were weighed. All these materials were mixed at speed of 1000 rpm in a speed mixer for 60 seconds at room temperature. The slurry is not easy to calend directly from the rollers without separating the water due to the large amount of water inside. After allowing to stand for 30 minutes, water may be leached to form a paste usable for calendering. Alternatively, after filtration through a filter paper to form a paste, the paste can be used for calendering on rollers.

3 is a SEM photograph of the paste by this one-step method. In this photograph, no fibers were found, only some agglomerated small particles and relatively large activated carbon particles were found. This confirms that during the one-step mixing process, the fibrillation of the PTFE is poor.

For roll calendering, a 2-roll calender was used. The calender nip was set to a width of 0.8 mm, and the mixed paste was passed through the nip. After rolling three times, the paste became a sheet. This sheet was folded in 1/3 and then inserted again into the nip of the calendar. This process was repeated eight times while changing the rolling direction at 90 ° each time. Finally, a uniform thin carbon composite sheet having a thickness of about 1 mm was prepared.

The tensile strength of the sheet produced by the one-step mixing method was 0.04 MPa, which was much lower than in Example 1.

4 shows a scanning electron microscope photograph of the carbon sheet produced by the above method. Compared to the photograph of FIG. 2, only a few fibers were close to the carbon particles. These fibers were produced in the calendering process because no fibers were found in the paste shown in the pre-calendering SEM photograph (Fig. 3).

Although the present invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Accordingly, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (29)

(a) providing a mixture of carbon particles and water plus carbon particles or water, and shearing the mixture to form a dispersion of the carbon particles or conductive particles in water;
(b) adding 2 to 10% (by dry weight) of poly (tetrafluoroethylene) to the dispersion by adding non-fibrillated poly (tetrafluoroethylene); 0 to 30% (by dry weight) of conductive material; And 60 to 98% (by dry weight) of carbon particles, wherein the weight ratio between water and the total amount of poly (tetrafluoroethylene), the conductive material and the carbon particles in the resulting mixture is 3 : 2 to 4: 1, and the resulting mixture is sheared until at least a portion of the poly (tetrafluoroethylene) is fibrillated, so that the resulting mixture forms a paste; Then
(c) processing the paste-like product mixture into a sheet; And
(d) attaching the sheet to the current collector
Wherein the electrode forming step comprises the steps of: The method according to claim 1,
Wherein in step (c) the product mixture is processed into a sheet by calendering. 3. The method according to claim 1 or 2,
Wherein steps (a) and (b) are carried out at room temperature, respectively. 3. The method according to claim 1 or 2,
Wherein said steps (a) and (b) are each carried out within a total of 30 seconds to 10 minutes. 3. The method according to claim 1 or 2,
Wherein the shear speed in each of steps (a) and (b) is 400 to 3500 rpm. The method according to claim 1,
Wherein the conductive material comprises a strongly acidic cation exchange resin. The method according to claim 1,
Wherein the conductive material comprises a strong basic anion exchange resin. The method according to claim 1,
Wherein the conductive material comprises carbon black or graphite powder. delete The method according to claim 1,
Wherein the non-fibrillated poly (tetrafluoroethylene) is added in portions into the fraction. The method according to claim 1,
Wherein the carbon particles comprise activated carbon particles. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

Images